1. Field of the Invention
The present invention relates to an adjusting device, and more particularly to an adjusting device for a tread board of a treadmill.
2. Description of Related Art
To adjust the angle of the tread board of a treadmill relative to the ground, an adjusting device is mounted on the treadmill. With reference to FIG. 7, a conventional adjusting-device for a tread board (40) of a treadmill comprises a stand (50), two connecting pieces (52), a thread rod (54), a sleeve (56) and a motor (58). One end of each connecting piece (52) is pivotally attached to one side of the tread board (40), and a connecting bar (not shown) is mounted between the other ends of the connecting pieces (52). Each connecting piece (52) has a middle point pivotally attached to the stand (50). One end of the thread rod (54) is pivotally attached to the connecting bar, and the other end of the thread rod (54) engages with an inner thread defined in the sleeve (56). The sleeve (56) is rotatably secured on the stand (50) and is connected to the motor (58). When the motor (58) is switched on, the sleeve (56) will rotate relative to the stand (50) and the thread rod (54) will move forward or backward relative to the sleeve (56). Consequently, the connecting pieces (52) will be pushed or pulled to pivotally rotate relative to the stand (50), and then the tread board (40) is lifted up or lowered.
However, because the sleeve (56) is rotatably secured on the stand (56), the sleeve (56) and the thread rod (54) cannot pivotally rotate relative to the stand (50). The thread (54) can only move in a straight travel, and the motor (58) is kept stationary during the operation of the conventional adjusting device. A large force will be applied to the thread rod (54) and the sleeve (56) to urge the thread rod (54) and the sleeve (56) to pivotally rotate relative to the stand (50) during the rotation of the connecting pieces (52). Therefore, the load bearing on the thread rod (54) and the sleeve (56) of the conventional adjusting device is very large such that the thread portions of the thread rod (54) and the sleeve (56) are easily damaged after a certain amount of use. In addition, because the motor (58) is mounted on the stand (50), a large space below on the tread board (40) is needed to arrange the adjusting device. Consequently, the lowest position of the tread board (40) is still at a certain height, and this causes the treadmill to be unstable in use.
To overcome the shortcomings, the present invention tends to provide an adjusting device to mitigate or obviate the aforementioned problems.